(1) Field of the Invention
This invention relates to a structural body for vehicles. More particularly, it relates to a vibration-damping rigid structural body which is integrally bonded by a thermal fusion-forming to a part of vehicle, which is subject to vibration such as a floor panel, a dash panel a wheel housing or ceiling panel.
(2) Description of the Related Art
A thermally fusible damping material predominantly comprised of asphalt has been popularly used for damping the vibration of a vehicle part such as a floor panel, a dash panel, a wheel housing or a ceiling panel, the material being fusion-bonded to the vibrating surface of the vehicle part. In recent years, an attempt has been made to provide a rigid metal sheet as a restraining material, such as a steel sheet or an aluminum sheet, on the asphalt damping material, or to laminate a layer of a thermosetting resin such as an epoxy resin, a diallyl phthalate resin or a thermosetting acrylic resin on the asphalt damping material, thereby forming a restraint type vibration-damping structure having a good vibration-damping property and a high rigidity.
Further, another attempt has been made to expand the asphalt damping material for enhancing the vibration-damping property.
However, the above-mentioned vibration-damping structures having the asphalt damping material have the following problems. Namely, a double layer-type vibration-damping structure, which is composed of a vehicle part and the damping material sheet predominantly comprised of asphalt and thermally fused on the vehicle part, must be sufficiently thick to obtain a vibration-damping property of the desired level. This leads to an increase in vehicle weight, and the double layer-type vibration-damping structure does not have a high rigidity. By using an expandable asphalt damping material, an increase in vehicle weight can be lowered, but the vibration-damping property cannot be enhanced to the desired level while the increase in vehicle weight is kept at a practically permissible low level.
In the case of the sandwich type vibration-damping structure wherein a rigid metal sheet such as a steel sheet or an aluminum sheet is laminated on the asphalt damping material layer, the vibration-damping property is satisfactory. To bond the rigid metal sheet as a restraining material to the thermally fused damping material layer, a means for mechanically fixing or screwing with a bolt the metal sheet to the rigid vehicle part is employed. However, the rigid vehicle part such as a floor panel usually has a press-molded shape, and therefore, a step of press-molding the restraining metal sheet into a shape corresponding to the shape of the press-molded vehicle part is needed. Further, it is troublesome to exactly position the restraining metal sheet to the vehicle part. Further, an attempt has been made wherein an uncured thermosetting resin is placed on the damping material and the uncured thermosetting resin is then cured during the step of drying a paint applied thereon, thereby forming a restraining material on the damping material. Another attempt has been made wherein a thermoplastic resin composition containing a tackifying resin as the matrix constituent is placed on the damping material and the thermoplastic resin is cured in the step of drying a paint applied thereon, thereby forming a restraining material. These attempts are useful for enhancing the vibration-damping property, but the need of abating noise within a vehicle is increasing more and more. Therefore, a vibration-damping structural body containing a resin restraining material, which exhibits a higher vibration-damping performance and has a higher rigidity with an increase in weight only of a practically acceptable extent is eagerly desired.